Attempt to identify the particular cell type(s) responsible for suppression of the immune response and to learn how these cells induce their suppressive effect using experimental models in mice. Attempt to identify the suppressor cells using selective removal of T and B lymphocytes and macrophages from tumorous lymphoid tissues. Determine whether or not the immunosuppressor cell (IsC) bears any marker of neoplastic transformation. Attempt to find a soluble product either free or membrane-bound, while studying the mechanism by which the IsC induce their suppressive effect. Study the alteration of the immune response of normal responder cells in the presence of IsC. Study the effect of IsC on helper T cell function, antibody response, and effector function of cytotoxic T cells and natural killer cells. Investigate the reversibility of suppression. Evaluate the metabolic and physiological characteristics of IsC and suppressed responder cells.